The strontium isn't reinforcement but rather, a grain refiner. It gives a finer grained solidification microstructure. This gives some improvement in mechanical properties:
Actually, there is a large percentage of casting alloys that are obtained via recycling even in North America. All of those automotive engine blocks, heads, etc. that are reclaimed from junkyard vehicles are part of a very well integrated recycling chain. Only ~ 25% of the mass of an automobile is not recycled, and that is almost entirely the non-metallic stuff (tires, foam, upholstery, etc.).